Metabolic Bone Disease - Calcium Deficiency

by the Winter Park Veterinary Clinic

1601 Lee Road

Winter Park Florida 32789

(407) 644-2676

(Revised 6/96)

Disclaimer:The Winter Park Veterinary Clinic has given me (Catherine Rigby) permission to reproduce this clinic handout on-line with the understanding that the clinic may have a newer version of this document with more up-to-date information that will render this on-line version no longer concurrent with the hardcopy information the clinic distributes.

Reptile information is continually being updated as more is learned, and the Winter Park Clinic makes it a practice to keep their handouts as up-to-date as possible.

Calcium deficiency leading to metabolic bone disease is the most common illness seen in reptiles presented to our clinic. Most cases result from malnutrition -- specifically, a diet with no calcium whatsoever. Because calcium metabolism is so complex, treatment consists of more than just adding calcium to the diet.

Calcium is a mineral necessary for normal neuromuscular function, blood clotting, activation of certain enzymes, heart contraction and bone structure. Reptiles often obtain calcium in their diet. a healthy intestine, kidneys and liver, and vitamin D are all required for calcium absorption through the intestinal lining. Certain substances in the diet combine with calcium in the gut, making the absorption of calcium impossible; these include high fat levels, oxalates and acetic acid.

Phosphorous is a mineral that helps maintain normal acid-base equilibrium and is a component of both enzymes and bone. Calcium metabolism is directly affected by the relationship between calcium and phosphorous. This is expressed in a calcium to phosphorous ratio (ca:phos). a normal ratio is 1 to 2 parts calcium to 1 part phosphorous (1:1 to 2:1), both in the diet and in the body. Too much phosphorous in the diet reacts with calcium in the gut to form calcium phosphate, an unusable form of calcium. However, phosphorous continues to be absorbed into the body. This leads to a ca:phos ratio of less than 1:1 -- a calcium deficiency.

Vitamin D acts more like a hormone than like a vitamin. The source of vitamin D is either through the diet or by the action of ultraviolet light on the precursor molecules in the skin. Vitamin D is converted to an intermediate form in the liver, then to an active form in the kidneys. From there it acts in the intestine, facilitating calcium absorption there. It also moves into the bone to assist normal bone formation and mineralization. as you see, a healthy liver and kidneys are needed to activate vitamin D.

When insufficient levels of calcium exist in the blood, parathyroid hormone is secreted by the parathyroid glands, causing calcium resorption from the bone. This creates normal blood calcium levels at the expense of the skeleton and leads to weak, thin bone that fractures easily. Growth is stunted, and in some cases, excessive amounts of non-calcified scar tissue are deposited around the bones in an apparent attempt to support the structural weakness. This later condition is called fibrous osteodystrophy and is commonly seen as grossly swollen legs and jaws in iguanas.

To summarize, metabolic bone disease may be cause by:

Symptoms and treatment.

Symptoms of metabolic bone disease vary with age, duration of deficiencies, degree, and type of disease. Skeletal deformities include bowed legs, kinked backs, softness of the face and jaw (‘rubber jaw’) and irregular swelling of the limbs and jaw. Lameness results from fractures and bone deformities. Poor appetite occurs due to loose teeth and soft jaws. Fractured vertebrae can cause paralysis. Stunted growth is common. Spastic contraction of muscles can result. Remember, an apparently fat animal is not always well nourished.

Treatment involves correcting the diet, which is not always easy. Many reptiles (and not a few owners) are set in their ways and resist change. Patience and ingenuity are often required. When supplementing calcium, the ca:phos ratio must be kept in mind. Oral or injectable vitamin D may be given, and a good source of ultraviolet light must be provided (direct sunlight is best). Vitamin D must be in the form of D3 as other forms cannot be utilized. Check the ingredient panel of vitamin supplements to ensure D3 is used. Remember, vitamin D is a fat-soluble vitamin and is store din the body; hypersupplementation leads to toxicity. trying to quickly reverse a poor diet with hypersupplementation does not work -- it took a while for the bone disease to occur... it will take quite some time to reverse the damage.

Ultraviolet light can be provided by full-spectrum lights or by direct sunlight. (sunlight filtered through glass or plastic does not contain ultraviolet light... it has been blocked by the glass/plastic.)